In fluorine chemical industry, gas phase fluorination of halohydrocarbons is often used for preparation of hydrofluoroolefins and hydrochlorofluoroolefins, which has the following advantages: simple devices, easiness for continuous large-scale production, safety and the like. Fluorinated catalysts play a critical role in gas-phase fluorination reaction of halohydrocarbons. Presently, the catalysts for gas-phase fluorination used industrially are chromium-containing fluorinated catalysts.
Chinese Patent No. CN94106793.9 disclosed that a fluoride precursor was prepared by the precipitation of a mixture of Cr(NO3)3 and In(NO3)3 with ammonia water, and then the precursor was subjected to calcination and fluorination with HF to obtain a fluorinated catalyst composed of indium, chromium, oxygen and fluorine.
U.S. Pat. No. 5,773,671 disclosed that a blend of Al2O3 and Cr2O3 was impregnated in CoCl2 solution, and then subjected to drying, calcination, and fluorination to obtain a fluorinated catalyst.
EP0514932A3 disclosed that Cr2O3 with a specific surface area of more than 170 m2 g−1 was prepared by a precipitation method, and then subjected to fluorination to obtain a fluorinated catalyst. Moreover, it does not disclose the addition of other co-catalysts.
CN01141970.9 disclosed that an amorphous catalyst precursor with a specific surface area of more than 200 m2 g−1 and a pore volume of more than 0.3 m2 g−1 was prepared by reacting an aqueous solution of soluble salts of chromium and other components with a precipitant (an alkaline substance) at 20-100° C., and then subjected to calcination and activation to obtain a fluorinated catalyst of CrM0.3Mg0.1O0.5F2.0.
Catalysts for gas-phase fluorination used in practice are mostly chromium-containing catalysts. It has been demonstrated that chromium-containing compounds are toxic, and thus would damage human digestive tract and kidney. Moreover, high-valence chromium has a strong carcinogenic effect, and thereby production and use thereof would do harm to human and environment.
In order to solve the above-mentioned problems, the chromium-containing fluorinated catalyst needs to be replaced with a chromium-free fluorinated catalyst. For example, CN107817A and CN1111606A disclose a chromium-free catalyst, wherein zinc is loaded onto alumina, halogenated alumina or haloalumina, but the catalyst has a low catalytic activity. CN1680029A discloses a chromium-free catalyst, wherein an antimony halide (SbFnCl5-n) is loaded onto calcium fluoride, but the catalyst has a low catalytic activity. Moreover, the antimony halide is apt to run off during fluorination and the catalyst has a poor thermal stability.
In conclusion, the existing chromium-free catalysts have some drawbacks, such low activity, and easy running-off, and thus they have no practical value.